Turbomachine rotor assembly

ABSTRACT

A turbomachine rotor assembly comprising: a rotor disk ( 2 ) presenting slots ( 4 ) in its outer periphery; blades ( 14 ) fastened via their roots ( 16 ) in said slot ( 4 ); and shims ( 20 ) mounted between the blade roots ( 16 ) and the disk ( 2 ), each shim ( 20 ) comprising two branches ( 20 A) and a base part ( 20 B) interconnecting the branches, each branch ( 20 A) being disposed between the bearing surface ( 16 A) of a blade root ( 16 ) and the corresponding bearing surface ( 22 A) of the disk ( 2 ); each branch ( 20 A) being made of a first material presenting a first Young&#39;s modulus of value E, at any operating temperature in the operating temperature range of the shim ( 20 ). The rotor assembly includes pads ( 40 ) adhering to the bearing surfaces ( 22 A) of the disk and/or to the bearing surfaces ( 16 A) of the blade root, the pads ( 40 ) being made of a second material presenting a second Young&#39;s modulus of value lying in the range E/20 to E/5 at said operating temperature.

The invention relates to a turbomachine rotor assembly, of the type comprising: a rotor disk presenting slots in its outer periphery; blades fastened via their roots in said slot; and shims mounted between the blade roots and the disk, each shim comprising two branches and a base part interconnecting the branches, each branch being disposed between the bearing surface of a blade root and the corresponding bearing surface of the disk.

BACKGROUND OF THE INVENTION

The invention is applicable to any type of turbomachine whether for terrestrial or aviation purposes (turbojet, turboprop, terrestrial gas turbine, etc.). In the particular example of a bypass two-spool airplane turbojet, the invention can apply to the fan, to the low pressure compressor (or “booster”), to the high pressure compressor, to the high pressure turbine, or to the low pressure turbine of the turbojet.

In the present application, the axial direction corresponds to the direction of the axis of rotation A of the turbomachine rotor, and a radial direction is a direction perpendicular to the axis A. Furthermore, unless specified to the contrary, adjectives such as “inner” and “outer” are used relative to a radial direction such that the (radially) inner portion of an element is closer to the axis A than is the (radially) outer portion of the same element.

In a rotor assembly (i.e. an assembly forming part of the rotor) of the above-specified type, the (moving) blades are fastened to the disk of the rotor via fastener systems, that may be constituted by shank fasteners that are rectilinear or curved, hammerhead-shaped, or Christmas-tree-shaped. These fastener systems can be defined as devices in which the blade roots form the male portions of the system and are retained radially in the female portions of the system, which female portions are formed in the outer periphery of the disk and are commonly referred to as “slots”.

When the rotor is set into rotation, the blades are subjected mainly to centrifugal forces and also to axial aerodynamic forces, and the blade roots are pressed in abutment against portions of the disk lying on either side of the outer opening of each slot, under the effect of centrifugal forces. The surfaces of the blade roots and of the disks that come into abutment against each other are commonly referred to as “bearing surfaces”. These bearing surfaces are subjected to pressure (as a result of said forces applied to said bearing surfaces). To a first approximation, it can be estimated that this pressure depends on the square of the speed of rotation of the rotor.

It can thus be understood that the variations in the speed of rotation of the rotor during an operating cycle of the turbomachine: from stationary to full throttle, passing through various particular intermediate speeds (idling, taxiing, cruising, descending, for an aviation turbomachine), give rise to variations in the pressure acting on the above-defined bearing surfaces. These pressure variations associated with elastic deformations of the contacting parts give rise to relative movements between the blade roots and the disk. When they are repeated, these relative movements, known as slip or as separation depending on their nature, give rise to wear phenomena in the bearing surfaces of the blades or of the disks. It is also possible for the dynamic movements of the blades at a given speed of rotation (response of the blades to alternating stresses of harmonic or transient nature) to contribute to the phenomenon of said bearing surfaces becoming worn. These wear phenomena are naturally penalizing on the lifetime of a turbomachine.

Various so-called “anti-wear” solutions can be adopted, i.e. solutions that slow down the appearance of wear at the contact interfaces, and these solutions include those based on inserting a third body, referred to as “shim”, between the blade roots and the disk. The shim serves in particular to double the number of contact interfaces (going from a single blade/disk interface to a pair of interfaces, blade/shim and shim/disk), and to reduce the relative movements between the parts that are in contact, thus enabling wear to be reduced in operation.

A known example of shim of the above-mentioned type is described in document FR 2 890 684. That shim is made entirely out of metal, and it is constituted by a sheet of metal that is folded appropriately.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to provide a shim that is more effective than the above-mentioned known shim in terms of performing the “anti-wear” function, so as to provide better protection to the bearing surfaces of the blades and of the disk.

This object is achieved by a turbomachine rotor assembly of the type defined in the introduction, in which each branch is made of a first material presenting a first Young's modulus of value E, at any operating temperature in the operating temperature range of the shim, the rotor assembly including pads adhering to the bearing surfaces of the disk and/or to the bearing surfaces of the blade root, the pads being made of a second material presenting a second Young's modulus of value lying in the range E/20 to E/5 at said operating temperature.

It should be observed that the Young's modulus of a material varies as a function of the temperature of the material, and consequently that the values E and E′ depend on temperature.

The term “operating temperature” is used to mean the temperature to which the shim is subjected while the turbomachine is in operation under normal conditions of use. In the present invention, the relationship between said first and second Young's moduluses, as defined above, needs to be satisfied for all of the temperatures in the range of operating temperatures of the shim.

For example, when the shim belongs to the fan or to the low pressure compressor of a bypass two-spool airplane turbojet, its operating temperature lies in the range 20° C. to 150° C. When it belongs to the high pressure compressor of a bypass two-spool airplane turbojet, its operating temperature lies in the range 1500C to 500° C. When it belongs to the high pressure turbine of a bypass two-spool airplane turbojet, its operating temperature lies in the range 400° C. to 700° C.

The present invention thus relates to adopting said multilayer structure in which the (isotropic or anisotropic) elasticity characteristics of the second material are better than the (isotropic or anisotropic) elasticity characteristics of the first material in the desired operating temperature range.

In an embodiment, said first material is a metal alloy or an organic matrix composite material, while said second material is non-metallic. For example, and in non-exhaustive manner, the second material may be made of rubber, of silicone, of polyimide, of glass, or of epoxy resin.

The invention has the following effects:

-   -   uniformly distributing contact pressures by the pads         accommodating due to the elasticity of the second material;     -   during a change in speed of rotation, limiting relative         movements of the parts due to centrifugal forces by “static”         shear in said pads; and     -   damping any dynamic movements of the blade by “dynamic” shear in         said pads.

A particular consequence of these effects is to prevent or limit wear phenomena in the bearing surfaces, thereby increasing the lifetimes of blade roots and of disks.

These effects are reinforced when the second material presents viscoelastic behavior in the operating temperature range of the shim, more particularly for the purpose of damping any dynamic movements of the blade.

The invention also provides a turbomachine including such a rotor assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages can be better understood on reading the following detailed description. The description refers to the accompanying figures, in which:

FIG. 1 is a fragmentary exploded and diagrammatic view showing a turbomachine rotor assembly comprising a rotor disk, an example of shim in accordance with the invention, and a blade root;

FIG. 2 is a (fragmentary) radial section view on plane II-II of the FIG. 1 rotor assembly, once it has been assembled; and

FIG. 3 is a (fragmentary) section view analogous to that of FIG. 2 showing another example of a rotor assembly of the invention.

MORE DETAILED DESCRIPTION

FIGS. 1 and 2 show: a rotor disk 2 having numerous grooves or “slots” 4 in its periphery that define housings, each suitable for receiving the root 16 of a blade 14, the root 16 being surrounded by a shim 20. The blade root 16 and the fan disk 2 are made out of titanium alloy, for example.

It should be observed that assemblies also exist (not shown) that have a spacer placed between the blade root 16 and the bottom of the slot 4.

When the disk 2 is set into rotation, the blades 14 are subjected to centrifugal forces, and the bearing surfaces 16A on the blade root 16 become pressed against bearing surfaces 22A of the disk 2. In the example shown, the surfaces 16A constitute the flanks of the blade root 16, while the surfaces 22A constitute the bottom faces of the lip-shaped portions 22 of the disk that extend on either side of the outer opening of each slot 4.

The shim 20 has two side branches 20A for coming against the bearing surfaces 16A of the blade root 16 and a base part 20B, here a base plate, interconnecting the branches and extending under the blade root 16. Each branch 20A is made of a first material that at any temperature in the operating temperature range of the shim, presents a corresponding first Young's modulus of value E. The shim 20 is a wear piece having the main function of limiting wear of the blade root 16 and of the fan disk 2. The shim 20 needs to present a certain amount of stiffness in order to have adequate mechanical strength and perform its anti-wear function. Thus, the value of E is preferably greater than or equal to 110,000 megapascals (MPa) for a shim made of metal (e.g.: 210,000 MPa for shim made of a nickel-based superalloy, of the type sold under the name “Inconel”), and greater than or equal to 70,000 MPa for a shim made of an organic matrix composite material.

In accordance with the invention, the rotor assembly includes pads 40 that adhere to the bearing surfaces 22A of the disk, these pads 40 being made of a second material presenting a second Young's modulus of value lying in the range E/20 to E/5 at said temperature.

In other embodiments (not shown), pads are fastened on the bearing surfaces 16A of the blade root, or on both the bearing surfaces 22A of the disk and the bearing surfaces 16A of the blade root.

So far as the choice of materials is concerned, it naturally depends on the operating temperature of the shim.

When the rotor assembly belongs to the fan or the low pressure compressor of a bypass two-spool airplane turbojet, it is subjected to operating temperatures lying in the range 20° C. to 150° C. Under such circumstances, and by way of example, it is possible for the first material to be selected as a Ni-based superalloy with more than 15% by weight Fe and Cr, such as the superalloy sold under the name “Inconel 718”; while the second material can be rubber (natural or synthetic). In these circumstances, it is also possible for the first material to be a composite material using an epoxy resin matrix with reinforcing fibers, e.g. made of carbon; the second material could then be an epoxy resin on its own (with the difference in Young's modulus between the first and second materials being associated with the absence of fibers).

When the assembly belongs to the high pressure compressor of a bypass two-spool airplane turbojet, it is subjected to operating temperatures lying in the range 150° C. to 500° C. Under such circumstances, and by way of example, it is possible to select for the first material an Ni-based superalloy having more than 15% by weight of Fe and Cr, such as the superalloy sold under the name “Inconel 718”; the second material could be a silicone or polyimide.

When the assembly belongs to the high pressure turbine of a bypass two-spool airplane turbojet, it is subjected to operating temperatures lying in the range 400° C. to 700° C. Under such circumstances, and by way of example, it is possible for the first material to be selected as an Ni-based superalloy with more than 15% by weight Fe and Cr, such as the superalloy sold under the name “Inconel 718”; the second material may be glass (which in this operating temperature range presents viscoelastic behavior).

In general, it should be observed that the pads 40 can be fastened to the bearing surfaces 22A of the disk in various ways, and in particular:

-   -   by natural adhesion;     -   during polymerization of the pad (during its vulcanization it if         is made of rubber); or     -   by adhesive;     -   or by combining the above-mentioned techniques.

Naturally, the fastening obtained must be sufficient to prevent the pads 40 from detaching from the bearing surfaces 22A in operation.

FIG. 3 is a section view analogous to that of FIG. 2 showing (in part) another example of a rotor assembly 120 of the invention. Elements or element portions that are analogous between FIGS. 2 and 3 are identified by the same numerical references plus 100.

The example of FIG. 3 differs from that of FIG. 2 in that the base part 120B of the shim 120 extends over the outer periphery of the rotor disk 202, between two adjacent slots 204, with each branch 120A of the shim entering into a respective slot 204 and being received between the bearing surface 216A of the blade root 216 and the corresponding bearing surface 222A of the disk 202. The positions of the pads 140 remain the same. 

1. A turbomachine rotor assembly comprising: a rotor disk presenting slots in its outer periphery; blades fastened via their roots in said slots; and shims mounted between the blade roots and the disk, each shim comprising two branches and a base part interconnecting the branches, each branch being disposed between the bearing surface of a blade root and the corresponding bearing surface of the disk; each branch being made of a first material presenting a first Young's modulus of value E, at any operating temperature in the operating temperature range of the shim, said rotor assembly including pads adhering to the bearing surfaces of the disk and/or to the bearing surfaces of the blade root, the pads being made of a second material presenting a second Young's modulus of value lying in the range E/20 to E/5 at said operating temperature.
 2. A rotor assembly according to claim 1, in which said first material is a metal alloy or an organic matrix composite material, while said second material is non-metallic.
 3. A rotor assembly according to claim 1, in which said second material has viscoelastic behavior in the operating temperature range of the shim.
 4. A rotor assembly according to claim 1, in which the base part of each shim extends under a respective blade root.
 5. A rotor assembly according to claim 1, in which the base part of each shim extends over the outer periphery of the disk between two adjacent slots.
 6. A turbomachine including a rotor assembly according to claim
 1. 